1. Field of the Invention
The present invention relates to a positive resist composition suitable for use in microlithography processes such as the production of ULSIs or high-capacity microchips and in other photofabrication processes. More particularly, the invention relates to a positive resist composition capable of forming a high-resolution pattern with a vacuum ultraviolet light having a wavelength of 160 nm or shorter. The present invention also relates to a method of forming a resist pattern using the positive resist composition.
2. Description of the Related Art
The degree of integration in integrated circuits is increasing more and more, and it has become necessary to form an ultrafine pattern having a line width of a quarter micrometer or smaller in the production of semiconductor substrates for ULSIs or the like. One of the known techniques for enhancing the fineness of such patterns is to use an exposure light having a shorter wavelength in resist pattern formation.
For example, in the production of semiconductor elements having an integration degree of up to 64 megabits, the i-line (365 nm) from a high-pressure mercury lamp has hitherto been used as an exposure light. Many compositions comprising a novolak resin and a naphthoquinonediazide compound as a photosensitive substance have been developed as positive resists for use with the exposure light, and have given sufficient results in forming patterns having line widths down to about 0.3 μm. On the other hand, in the production of semiconductor elements having an integration degree of 256 megabits or higher, KrF excimer laser light (248 nm) has been used as an exposure light in place of the i-line.
Furthermore, use of ArF excimer laser light (193 nm), which is an exposure light having an even shorter wavelength, and use of F2 excimer laser light (157 nm) for forming a pattern having a line width of 0.1 μm or smaller are recently being investigated for the purpose of producing semiconductor elements having an integration degree of 1 gigabit or higher.
With the use of such exposure lights having shorter wavelengths, the components of resist materials and the structures of compounds for use therein are changing considerably.
A so-called chemical amplification type resist has been developed as a resist composition for exposure to KrF excimer laser light. This composition comprises a combination of: a resin, as the main component, having a poly(hydroxystyrene) backbone which shows reduced absorption in a 248 nm region and is protected by acid-dissociable groups; and a compound which generates an acid upon irradiation with far ultraviolet light (photo-acid generator).
Furthermore, another chemical amplification type resist has been developed as a resist composition for exposure to ArF excimer laser light (193 nm). This composition contains an acid-decomposable resin which has, incorporated in the polymer main chain or side chains thereof, alicyclic structures showing no absorption at 193 nm.
With respect to use with F2 excimer laser light (157 nm), even the alicyclic resin shown above was found to be insufficient in obtaining a desired pattern of 0.1 μm or finer because the resin shows considerable absorption in a 157 nm region. Under these circumstances, a resin having fluorine atoms (perfluorinated structure) incorporated therein was reported to have sufficient transparency at 157 nm, in Proceedings of the Society of Photo-Optical Instrumentation Engineers (Proc. SPIE), Vol. 3678, p. 13 (1999). Effective structures of such fluororesins are proposed in
Proceedings of the Society of Photo-Optical Instrumentation Engineers (Proc. SPIE), Vol. 3999, p. 330 (2000), Proceedings of the Society of Photo-Optical Instrumentation Engineers (Proc. SPIE), Vol. 3999, p. 357 (2000), Proceedings of the Society of Photo-Optical Instrumentation Engineers (Proc. SPIE), Vol. 3999, p. 365 (2000), and WO-00/17712, pamphlet. Resist compositions containing a fluorine-containing resin have been investigated.
However, none of those resists satisfies various performances including transparency at 157 nm, sensitivity, and resolution. Those resists have further had a problem that they show poor evenness of application and poor resistance to dry etching.